The objectives of this study are: 1. To evaluate the hypothesis that risk of Hodgkin's disease is a function of factors in childhood environment which inhibit infectious transmission; in particular family size, birth order, and social class. 2. To re-evaluate the association of tonsillectomy and risk of Hodgkin's disease. 3. To evaluate occupational exposures and risk of Hodgkin's disease. 4. To establish a serum bank. A two part case-control study is proposed. In Part I, conducted in the Boston and Worcester, Massachusetts SMSA's, essentially all incident cases of a four-year period will be identified. Controls will include siblings of cases as well as persons selected from the general population. Information will be gathered by home interview and blood specimens drawn from cases and siblings. Part II will be conducted by mail questionnaire in the Detroit, Michigan metropolitan area. A similar case series will be identified and their siblings used as controls.